Field of the Invention
The present invention relates to control valves and balancing valves commonly used in hydronic systems to monitor and adjust fluid flow rate and ensure a relatively steady flow of fluid through the system. The invention provides a control valve incorporating a novel design of balancing mechanism which results in better performance of a hydronic system when the improved valve is incorporated.
Background Art
In fluid networks, it is common to distribute fluid from a source to one or more points of consumption (loads). In order to provide the correct amount of fluid under varying demands, one or more control valves are commonly provided. These control valves respond to a control signal to create variable restrictions in the system providing an appropriate amount of fluid to each load. For example, the control signal might be supplied by a thermostat, and the valve would respond by changing the flow of heating or cooling fluid through a heat exchanger. If these control valves are chosen with a maximum opening that is larger than the maximum needed for the application, then they must be controlled to close excessively at all times. This excessive closure results in unstable control as the control valve changes from an open to a closed condition repeatedly rather than settling at the proper location. Conversely, if the valve is chosen with too small a maximum opening, excessive pumping energy is required to address unnecessary pressure drops arising in the system. This problem is compounded by the fact that control valves are ordinarily available only in fixed steps, forcing the user to select one or another type of error.
These systems also normally have differing amounts of surplus pressure at different terminals. An ordinary control valve provides no means for reading the flow rate of the fluid, nor of manually adjusting its maximum opening which will cause an ordinary control valve to flow incorrectly. While the amount of surplus pressure might be calculated in theory, in practice the calculations are often not done due to their complexity, or are inaccurate due to construction variations. This problem is frequently addressed by installing balancing valves, which provide a calibrated adjustable restriction and a means of measuring the flow rate. A balancing contractor is then employed to adjust these balancing valves throughout the system so that at maximum flow conditions all terminals receive the correct flow of fluid without excess.
A limitation of current techniques is that the restriction created by the balancing valve is not taken into account by the control valve, so that a portion of the control valve's stroke is wasted.
Some prior devices combine the function of a control valve and a balancing valve in a single unit, providing improved performance of the combined unit. With the control function and balancing accomplished by a single device, it is possible to provide improved control performance tailored to the exact conditions experienced at a given terminal.